Light pads are thin surfaces fitted with arrays of small LEDs and may typically be used for tracing and drawing applications. Strangely they are sometimes advertised as being suitable for viewing X-Ray images (is this a common need outside a hospital?) and this may suggest that they would also work for viewing photographic negatives.
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| Light Pad |
However there is a problem, the surface is shiny and prone to specular reflections, you can see the reflection of my LED OttLite desk lamp in the image above. Even worse is that the array of LEDs shows through when trying to back light an image, so for example here is how a colour slide (positive) looks:
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| Slide viewed directly with LED array showing |
Not very good but the solution is actually very simple, a layer of diffusion material is needed and this can be done with a sheet of paper. The paper should not be coloured and should be thin, I found a sheet of 41gsm tracing paper works well. To see the difference this makes here's the same slide, now sitting above a sheet of paper:
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| Slide viewed with sheet of paper as a diffuser |
This is a big improvement and makes a cheap light pad into a potentially viable light box. It also works with negative film strips:
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| Viewing a 35mm negative film strip |
A viewing loupe may also prove helpful for checking the smaller details. Although I only occasionally need to view film negatives I do have a number of old family slides to review for scanning but my main purpose in wanting a light box is to view and check digital negatives. Here is an example of a digital negative prepared for contact printing onto Cyanotype.
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| Viewing a digital negative |
So for viewing up to A4 size this type of low cost LED based light pad can make a reasonable solution with the addition of a simple sheet-of-paper diffuser.
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